Scientists show large impact of controlling humidity on greenhouse gas emissions

Date:
March 15, 2022
Source:
DOE/National Renewable Energy Laboratory
Summary:
Greenhouse gas emissions from air conditioners are expected to climb
as economic growth drives efforts to control both temperature and
humidity, according to a new analysis.



FULL STORY ========================================================================== Greenhouse gas emissions from air conditioners are expected to climb as economic growth drives efforts to control both temperature and humidity, according to an analysis by scientists from the National Renewable Energy Laboratory and Xerox PARC.


==========================================================================
The research, which explores the environmental impact of controlling
humidity, appears in the journal Joule as "Humidity's impact on greenhouse
gas emissions from air conditioning." While the energy used to power
air conditioners has clear implications on greenhouse gas emissions,
the impact from removing moisture from the air has escaped in-depth
study until now. The researchers showed that controlling humidity is responsible for roughly half of the energy- related emissions, with the
other half due to controlling temperature.

"It's a challenging problem that people haven't solved since air
conditioners became commonplaces more than a half-century ago," said
Jason Woods, an NREL senior research engineer and co-author of the new
study. His co-authors from NREL are Nelson James, Eric Kozubal, and Eric Bonnema. The collaborators from Xerox PARC, an R&D company working on
ways to remove humidity more efficiently from the air, are Kristin Brief,
Liz Voeller, and Jessy Rivest.

The researchers pointed out the increasing need to cool the air is both
a cause and an effect of climate change.

Even a small amount of moisture in the air can cause people to feel uncomfortable and even damage buildings in the form of mold and mildew.

Furthermore, controlling indoor humidity through commercially available
air conditioning technologies impacts the environment in three ways: 1)
They consume a considerable amount of electricity, 2) they use and leak CFC-based refrigerants with global warming potential that is 2,000 times
as potent as carbon dioxide, and 3) the manufacturing and delivery of
these systems also release greenhouse gases.

The researchers calculated air conditioning is responsible for the
equivalent of 1,950 million tons of carbon dioxide released annually,
or 3.94% of global greenhouse gas emissions. Of that figure, 531 million
tons comes from energy expended to control the temperature and 599
million tons from removing humidity. The balance of the 1,950 million
tons of the carbon dioxide come from leakage of global-warming-causing refrigerants and from emissions during the manufacturing and transport of
the air conditioning equipment. Managing humidity with air conditioners contributes more to climate change than controlling temperature
does. The problem is expected to worsen as consumers in more countries -- particularly in India, China, and Indonesia -- rapidly install many more
air conditioners.



========================================================================== "It's a good and a bad thing," Woods said. "It's good that more people
can benefit from improved comfort, but it also means a lot more energy is
used, and carbon emissions are increased." To calculate the emissions
to manage both temperature and humidity, the researchers divided the
globe into a fine grid measuring 1 degree of latitude by 1 degree
of longitude. Within each grid cell, the following characteristics
were considered: population, gross domestic product, estimated air
conditioner ownership per capita, carbon intensity of the grid, and
hourly weather. They ran nearly 27,000 simulations across the globe for representative commercial and residential buildings.

Climate change is affecting ambient temperatures and humidity around
the globe, making it warmer and more humid. As part of the study,
the researchers considered the impact of the changing climate on air conditioner energy use by 2050. For example, the study projects air
conditioner energy use to increase by 14% in the hottest climate studied (Chennai, India) and by 41% in the mildest (Milan, Italy) by 2050. The
increase in global humidity is projected to have a larger impact on
emissions than the increase in global temperatures.

"We've already made the existing, century-old technology nearly as
efficient as possible," Woods said. "To get a transformational change
in efficiency, we need to look at different approaches without the
limitations of the existing one." Existing vapor compression technology
is optimized to cool our buildings using a "vapor compression cycle." This cycle uses harmful refrigerants to cool air down low enough to wring out
its moisture, often over-cooling the air and wasting energy. Improving
the vapor compression cycle is reaching practical and theoretical limits,
thus pointing to a need to leap-frog to an entirely new way to cool
and dehumidify buildings. New technologies that split this cooling and
humidity control problem into two processes show potential to improve efficiency by 40% or more. Once such technology space is the use of
liquid desiccant-based cooling cycles such as the many liquid desiccant
air conditioning technologies that NREL is currently developing with
many partners, such as Emerson and Blue Frontier.

The researchers point out that the use of liquid desiccants fundamentally changes the way humidity is controlled and has theoretical efficiency
limit that is 10 times higher than the vapor compression cycle alone. A hypothetical technology -- at only half this new limit -- would reduce cooling-energy emissions by 42% in 2050, with the equivalent of avoiding
2,460 million tons of carbon dioxide annually.

The Department of Energy's Building Technologies Office funded the
research published in Joule.


========================================================================== Story Source: Materials provided by
DOE/National_Renewable_Energy_Laboratory. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Jason Woods, Nelson James, Eric Kozubal, Eric Bonnema, Kristin
Brief, Liz
Voeller, Jessy Rivest. Humidity's impact on greenhouse gas emissions
from air conditioning. Joule, 2022; DOI: 10.1016/j.joule.2022.02.013 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220315121427.htm

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